Project Summary Glutamate is the major excitatory neurotransmitter in the brain. The development and function of glutamatergic synapses is essential for proper neuronal connectivity and brain function, including learning and memory. Recent data suggest that defects in synapse development and function contribute to several neurodevelopmental and neuropsychiatric diseases such as intellectual disability, autism spectrum disorders, Alzheimer's disease and schizophrenia. In addition, excessive activation of glutamate signaling can lead to excitotoxic cell death in ischemia, stroke and neurodegenerative diseases. Thus, it is important to understand the cell biological and molecular mechanisms involved in regulating glutamatergic synapses. While much progress has been made identifying genes that regulate glutamatergic synapse development and function in vitro using neuronal cultures, less is known about the in vivo function of many of those genes. Challenges of in vivo analysis include the fact that mouse gene knock-outs do not always lead to the same dramatic synaptic defects observed in vitro, perhaps due to gene redundancy, and furthermore, compound knock-outs of gene families often lead to embryonic lethality further hindering phenotypic analyses. We use C. elegans as a genetic model to study genes and mechanisms that regulate glutamatergic synapses in vivo. Advantages of C. elegans include less gene redundancy, powerful genetic tools, a simple defined nervous system, and the ability of the animal to tolerate severe reductions in neuronal function. The goal of this exploratory proposal is to identify novel genes and mechanisms that regulate glutamatergic synapse development and function in vivo. In Aim 1, we combine several strengths of C. elegans and develop an innovative, optogenetic behavioral screen, based on a simple glutamatergic behavior, to identify conserved neuronal genes that regulate glutamatergic synapes. We have completed a pilot screen of genes with cell-adhesion molecule domains and identified several strong candidates, including the Ig-domain-containing, VEGF (Vascular Endothelial Growth Factor) receptor-related genes, ver-1 and ver-4. In Aim 2, we investigate the role of ver-1 and ver-4 in regulating glutamatergic synapses to illustrate our strategy for analyzing top candidates from our screen. Understanding how VEGFR signaling regulates glutamatergic synapses in C. elegans will be informative given that worms do not possess a cardiovascular system where VEGF has traditionally been shown to act. Identifying novel genes and fundamental mechanisms that regulate glutamatergic synapses may provide potential therapeutic targets for treatment of neurological diseases.